Reaction of O atoms with

Becker and Bayes made a more detailed investigation of the chemilumines- 

The details of reaction (17) could not be resolved, but a possibility is a sequence of steps such as 

This is consistent with the observation that at low [O], the NO emission intensity depended quadratically on [0]. An unexplained observation was that the NO emission increased with O atom concentration, passed through a maximum, and then declined with further increase in [O]. 

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Flowever, in order to deliver on its promise and maximize its impact on the broader field of chemistry, the methodology of reaction dynamics must be extended toward more complex reactions involving polyatomic molecules and radicals for which even the primary products may not be known. There certainly have been examples of this notably the crossed molecular beams work by Lee [59] on the reactions of O atoms with a series of hydrocarbons. In such cases the spectroscopy of the products is often too complicated to investigate using laser-based techniques, but the recent marriage of intense syncluotron radiation light sources with state-of-the-art scattering instruments holds considerable promise for the elucidation of the bimolecular and photodissociation dynamics of these more complex species. 

The existence of two modes of reaction of O atoms with N02, reactions (35) and (6) may be explained similarly... 

A surface pretreated with KC1 would make the reaction of O atoms with hydrocarbons flameless. As it was suggested that hydroxyl was formed in the flame, the vessel was coated with KC1. Selective disappearance of hydroxyl in great amounts was known to occur on a surface coated with KC1.18 As a result, the reaction chain terminated and the reaction became flameless. However, this result was not immediate. 

Product Formation Rates for Reactions of O Atoms with Unsaturated Hydrocarbons... 

The similar behavior of CO and CHO in reactions 0 + C2H and O + C2H provided confirmation to the conclusion that the same CH2 radical is formed by the primary steps of these reactions. In an earlier work4 (using discharge in H20 vapor involving less 02 molecules in the reaction vessel), the formation of CH2 in a reaction of O atoms with C2H4 was evident from its effect on a tellurium mirror. The reaction yielding... 

CH20 by reaction with 02. The amount of hydrogen peroxide was comparable to that of CH20. Under conditions of the 0 + CH3OH reaction the amount of hydrogen peroxide was by a power of ten less than that of CH20, which is evidence for the small importance of reaction (17). Thus, the reaction of O atoms with CH3OH will be either that of (18) or that of (19). It cannot be said so far which of these two is of more importance. Reactions of the (18) and (19) type were observed for other molecules. Reaction of the (18) type is similar to that of 0 atoms with CH4, while a reaction of the (19) type would be similar to known incorporation reactions. 

The reaction of O atoms with acetaldehyde shows that the three possible types of oxygen atom reactions are scission of the C-C bond, the reaction yielding H20, and incorporation of the 0 atom at the C-H bond. 

Reaction of Oxygen Atoms with Hydrogen. The possible reactions of O atom with H2 are... 

Old-bond excitation may have been observed in infrared region emission studies of the reaction of O atoms with N0258. Interference spectrometry techniques have been used to examine the infrared emission that occurs when O (presumably 3P) is mixed with NO or N02, the reactions being... 

This is probably because 0 atoms produced in primary process (45) react much more rapidly with C2H6 than with N20. Several products are formed including ethylene, butane, carbon monoxide, hydrogen, methane, and probably ethanol and acetaldehyde. More ethylene is formed than one would expect from the amount of butane. It was found that 0 atoms react rapidly with ethylene, which is one of the photolytic products. The reaction-rate constant of O atoms with ethylene is estimated to be about 330 times as rapid as that with ethane.82 Complete elucidation of the mechanism of O-atom reaction with ethane is complicated because of the rapid reaction of O atoms with one or more of the products. 

Several diatomic species are electronically excited in the reaction of O atoms with C2H2, and their spectra have been observed in flame [169, 170],... 

Following the conclusions of Bowman [1], then, from the definition of prompt NO, these sources of prompt NO in hydrocarbon fuel combustion can be identified (1) nonequilibrium O and OH concentrations in the reaction zone and burned gas, which accelerate the rate of the thermal NO mechanism (2) a reaction sequence, shown in Fig. 7, that is initiated by reactions of hydrocarbon radicals, present in and near the reaction zone, with molecular nitrogen (the Fenimore prompt-NO mechanism) and (3) reaction of O atoms with N2 to form N2O via the three-body recombination reaction,... 

REACTIONS OF O ATOMS WITH SULFUR COMPOUNDS 3.1.1 Reactions with SO... 

Sharma et al. measured the rate of the chemiluminescent step, reaction (2), in a flow system. For this measurement they produced their SO by the reaction of O atoms (produced from the electrical discharge of O2 or 02-Ar mixtures) with OCS. They also conducted experiments in which the SO was produced by the reaction of O atoms with H2S. The details of this reaction are discussed below here we note only the conclusions pertinent to the OH-SO reaction. They found that the initial intensity of the afterglow in both systems (OH-OCS and O-I-H2S) increased linearly with time at constant reactant pressures, was proportional to [O] when the other reactant pressure was held constant and was linearly proportional to [H2S] or [OCS] when [O] was held constant. 

RATE COEFFICIENTS FOR REACTIONS OF O ATOMS WITH SOME SULFUR COMPOUNDS... 

Two approximate measurements have been reported for the reaction of O atoms with sulfur trioxide... 

Sharma et in work described earlier, found the relative emission intensity of the reaction of O atoms with H2S to be 1.85 times greater than that for the reaction of O-fOCS. Using the value of determined by Sullivan and Warneck . they thus calculated a value of k = 1.02 x 10 l.mole . sec for the rate of that part of the reaction of O-I-H2S which leads to SO production. They stated that their value was a factor of 6 smaller than the result reported by Liuti et al. which they quote as being 6x 10 l.mole sec"S However, Liuti et al. obtained 1.2 X 10 l.mole sec for the overall rate coefficient, and since the chain reaction, which formed SO, accounted for 80 % of the reaction, the discrepancy between the two sets of workers is closer to a factor of ten. Sharma et al. suggest that the condition of the walls may account for the discrepancy if for some reason the disappearance of HS at the walls was greater in one of the experiments, then the production of SO would have been different, and so would the inferred rate coefficient for the overall reaction of O -I- H2S. At present, there does not seem to be any other explanation for the disagreement in the results. 

REACTIONS OF O ATOMS WITH NITROGEN COMPOUNDS 5.1.1 Reaction of O atoms with NH3... 

Moore et studied the reactions of O atoms with NH3 and N2H4 in atomic flames. The emission observed from the NH3 + O flame was very weak compared... 

The conclusion was at variance with the findings of Jackson " , who could not detect CO2 formation, but found ozone to be the only product. He concluded that the reaction of O atoms with CO must be at least 150 times slower than with O2. In his experiments, O atoms were formed by photodissociation of O2 with an aluminum spark (A, > 1719 A). Groth ", in similar experiments but with a Xe lamp (X = 1470, 1296 A), found the rate coefficient for reaction of O atoms with CO to be 1/40 of that with O2. 

The concentration of HO2 obtained from the H + H2O2 reaction at a pressure of about 0.5 mm. of Hg and reaction time of about 0.01 second was of the order of 0.1%. The reaction of O atoms with H2O2 was found to generate HO2 radicals, but at substantially lower concentration. The reaction involved is... 

With the exception of iodomethane (CH3I) and neopentyl iodide ((CH3)3CCH2l) all the reactions of 0( P) with the alkyl iodides were found to produce as major product an alkene. An example is shown for 1-iodobutane in Figure 9. Hypoiodous acid (HOI), the probable coproduct in each case, was also identified via its known infrared absorptions at 3620 and 1070 cm (Bames et al., 1992). This compound is, however, very short-lived under the conditions of the experiments and was only visible in the infrared spectrum in the initial stages of the reaction (Figure 10) and could therefore not be quantified. For many of the alkenes calibrated reference spectra were available and the yield of the alkene has been determined. Oxygen atoms also react fairly rapidly with alkenes, therefore, the reaction of O atoms with the alkenes has been taken into consideration when calculating the alkene yields from the O + Rl reactions. The yields and the identity of the alkene for the respective O + RI reactions are listed in Table 1. 

It is interesting to compare the alkenes formed in the reactions of 0( P) with 1-iodobutane and 2-iodobutane. In the reaction of O atoms with 1-iodobutane only one aUcene can be formed, namely 1-butene, and this is observed with a yield of around 70%. In the case of 2-iodobtane, however, there is the possibility of the formation of both 1-butene and cisitrans -2-butene as the major alkene product (see Figure 11). The measurements show that the major alkene is 1-butene with a yield of around 46%. This results implies that adduct formation of the O atom between the I atom and the terminal methyl group is favoured over adduct formation between the O atom and the methylene group. Formation of trans-2-butene was observed, however, the yield was difficult to quantify and only a limit of <10% can be set at present. 

Under collaboration between FC, UI and the Bergische University Wuppertal, experimental studies of the atmospheric chemistry of C3 to C5 alkyl iodides have been performed in the EUPHORE outdoor chamber in Valencia, Spain. The kinetics and mechanism of the reactions of O atoms with alkyl halides have also been investigated. 

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